• Title/Summary/Keyword: vibration modes

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A Study on Vortex-Induced Vibration Characteristics of Hydrofoils considering High-order Modes (고차모드를 고려한 수중날개 와류기인 진동특성 연구)

  • Choi, Hyun-Gyu;Hong, Suk-Yoon;Song, Jee-Hun;Jang, Won-Seok;Choi, Woen-Sug
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.28 no.2
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    • pp.377-384
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    • 2022
  • Vortex-induced vibration (VIV) occurs owing to the vortex generated from the back side of the appendages of ships and submarines during operation. Recently, the importance of high-order modes (HOMs) vibration and fatigue failure has become increasingly emphasized by increasing the speed of ships and the size of structures. In addition, predicting the vibration of HOMs is significantly necessary as the VIV becomes stronger in the fast flow speed condition than in the low flow speed condition. This study introduces a methodology according to HOMs hybrid Fluid Structure Interaction (FSI) for predicting the HOMs VIV on the hydrofoils. The HOMs FSI system is verified by comparing the VIV results from the FSI simulation with the experimental results. Finally, the effectiveness of the HOMs FSI is determined by applying the maximum von-Mises stress obtained from the VIV on the hydrofoil to the S-N curve released from Det Norske Veritas (DNV). VIV results from the HOMs FSI include the lock-in characteristics as well as a significant increase of more than 10 times compared with that of low-order modes (LOMs) FSI. In the future works, advanced studies will be required for improving cantilever boundary conditions and the shape of hydrofoils.

Experimental Modal Analysis for 3-D Vibration Characteristics of Radial Tire for Passenger Car under Free-Suspension (실험모드해석에 의한 승용차용 레디얼 타이어의 3차원 진동특성)

  • 김용우;남진영
    • Transactions of the Korean Society of Automotive Engineers
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    • v.10 no.3
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    • pp.227-236
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    • 2002
  • We have performed two kinds of experimental modal analyses fur a radial tire for passenger car under free-suspension. One is the modal analysis to obtain three-dimensional modes of tire using accelerometers and the other is the one to identify cavity resonance frequency using a pressure sensor. From the first analysis, we have obtained the three-dimensional natural modes, which makes it possible to grasp the features of the modes and to classify the vibrational modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the first and the second experimental analyses we have identified the cavity resonance frequency and its three-dimensional mode shape.

Optimal Control of Large Flexible Structures Via Partial Decoupling (부분 분리법에 의한 유연성이 있는 대형구조물의 최적제어)

  • Jeon, Gi-Joon
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.23 no.2
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    • pp.189-196
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    • 1986
  • Linear second-order matrix systems representing dynamics of large flexible structures are recast in a state space form. By can efficient partial decoupling technique, a few of low frequency modes are decoupled from the rest of modes, and an optimal control procedure is developed in such a way that damping is added to the selected modes without control spillover to uncontrolled modes. Since the partial decoupling requires only eigenvectors of the sected modes, the computing time can be reduced significantly in large systems. Therefore, the method of partial decoupling and control developed in this work may be applicable to vibration contorl of large flexible space structures.

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Active Control of Clamped Beams Using Acceleration Feedback Controllers (가속도 되먹임 제어기를 이용한 양단지지보의 능동제어)

  • Shin, Chang-Joo;Hong, Chin-Suk;Jeong, Weui-Bong;Jeong, Sang-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2010.10a
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    • pp.101-109
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    • 2010
  • This paper reports active control of clamped beams using acceleration feedback controllers (AF). The equations of motion of clamped beam under force and moment pairs were derived and the equations of AF controllers were formulated. The effect of the parameters - gain and damping ratio - of the AF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the AF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies. The increase of the damping ratio of the AF controller leads to decrease the magnitude of the open loop transfer function and modifies its phase characteristics to be more stable. Three AF controllers connected in parallel were then proposed. Each AF controller is tuned at the $2^{nd}$, $3^{rd}$ and $4^{th}$ modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the 3 modes can be obtained.

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Model Validation and Controller Design for Vibration Suppression of Flexible Rotor Using AMB

  • Soo Jeon;Ahn, Hyeong-Joon;Han, Dong-Chul
    • Journal of Mechanical Science and Technology
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    • v.16 no.12
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    • pp.1583-1593
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    • 2002
  • This paper discusses the model validation and vibration suppression of an AMB flexible rotor via additional LQG controller. The main difficulty in the vibration suppression of the flexible rotor using AMB is to realize a controller that can minimize resonance without injuring the stabilized rigid modes. In order to solve this problem, simple scheme for system modeling and controller design are developed. Firstly, the AMB flexible rotor is stabilized with a PID controller, which leads to a new stable rotor-bearing system. Then, authors propose the model validation procedure using measured open-loop frequency responses to obtain an accurate model of the AMB flexible rotor system. After that, LQG controller with modal weighting is designed to suppress resonances of the stable rotor-bearing system. Due to the poor controllability and observability of flexible modes compared to rigid ones, balancing of two Gramians is prerequisite for the fair LQG controller design. Simulation with step disturbance and experimental results of unbalance response up to 10,000 rpm verified the effectiveness of the proposed scheme.

Multi-Modal Vibration Control of Laminated Composite Plates Using Piezoceramic Sensors/Actuators (압전감지기/작동기를 이용한 복합적층판의 다중모드 진동제어)

  • Kim, Mun-Hyeon;Gang, Yeong-Gyu;Park, Hyeon-Cheol;Hwang, Un-Bong;Han, Gyeong-Seop
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.10
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    • pp.3173-3185
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    • 1996
  • Multi-model vibration control of laminated composites plates for various fiver orientations has been carried out by making use of piezolectric materials(PZT) as sensors and actuators. Cantilever plate is used as a specimen to test multi-modal vibration supression under random exitation. Impulse technique is applied to determine the natural frequency, the damping ratio(.zeta.) and the modal damping(2.zeta..omega.) of the first bending and the trosion modes. Two independent controllers are implemented to control the two modes simultaneously and established digitally on the basis of the direct negative velocity feedback control with collocated sensor/actuator. Experimental results for various fiber orientations and feedback gains are compared with finite element analysis considering stiffnesses and dampings of piezoeletiric sensors, actuators and bonding layer.

A Study on Vibration Characteristics of Flywheel Energy Storage System Using Superconducting Magnetic Bearings (초전도자기베어링을 이용한 플라이휠 에너지 저장장치의 진동특성에 관한 연구)

  • 김종수;이수훈
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.2
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    • pp.170-177
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    • 1998
  • The purpose of superconducting magnetic bearing flywheel energy storage system(SMB-FESS) is to store unused nighttime electricity as kinetic energy and convert it to electricity during daytime. The SMB-FESS is proposed as an efficient energy storage system because there is no mechanical problems, such as friction and wear The flywheel over SMB is rotated at a high speed, 50,000rpm. The major source of energy loss in the SMB-FESS is vibration of flywheel. Therefore, the vibration characteristics of SMB-FESS should be identified. In this study, the axial/radial stiffness and damping coefficient of SMB are measured by a vibration test. Natural frequencies and natural modes of flywheel and magnet are analyzed by a finite element method. The modal analysis of system is performed using the modal parameters of each component and the measured stiffness/damping coefficient. So, natural at frequencies and mode shapes of the joined system can be obtained. According to critical speed analysis, the system has two rigid conical modes in the low speed range. Nevertheless, the system has not been affected by the critical speed in the main operating range.

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A method to evaluate the frequencies of free transversal vibrations in self-anchored cable-stayed bridges

  • Monaco, Pietro;Fiore, Alessandra
    • Computers and Concrete
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    • v.2 no.2
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    • pp.125-146
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    • 2005
  • The objective of this paper is setting out, for a cable-stayed bridge with a curtain suspension, a method to determine the modes of vibration of the structure. The system of differential equations governing the vibrations of the bridge, derived by means of a variational formulation in a nonlinear field, is reported in Appendix C. The whole analysis results from the application of Hamilton's principle, using the expressions of potential and kinetic energies and of the virtual work made by viscous damping forces of the various parts of the bridge (Monaco and Fiore 2003). This paper focuses on the equation concerning the transversal motion of the girder of the cable-stayed bridge and in particular on its final form obtained, restrictedly to the linear case, neglecting some quantities affecting the solution in a non-remarkable way. In the hypotheses of normal mode of vibration and of steady-state, we propose the resolution of this equation by a particular method based on a numerical approach. Respecting the boundary conditions, we derive, for each mode of vibration, the corresponding frequency, both natural and damped, the shape-function of the girder axis and the exponential function governing the variability of motion amplitude in time. Finally the results so obtained are compared with those deriving from the dynamic analysis performed by a finite elements calculation program.